Considering fuel efficiency of an automobile and the like using tires, low rolling resistance of the tires is desirable and, in order to reduce the rolling resistance, low hysteresis loss (tan δ) of tread rubber of the tires is desirable.
In general, hysteresis loss of tread rubber has a tendency to be low on an inner side and becomes higher as it approaches a surface. Such a tendency has been one of factors that rolling resistance of a new tire (at the time of initial use) increases.
Although there is a known technique to reduce the tendency by lowering vulcanization temperature, the technique has problems such as generating a difference in the rolling resistance in a thickness direction and having a great impact on production efficiency.
Further, in order to deal with a great difference in a vulcanization temperature rising rate between the surface and the inner side during vulcanization, there is disclosed a technology of manufacturing equipment that, by using a dedicated manufacturing equipment that produces unvulcanized rubber having a structure in which rubber is sequentially distributed according to a vulcanization temperature rising distribution; that is, having slow-vulcanized rubber arranged near the surface where temperature rises quickly and fast-vulcanized rubber arranged the inner side where temperature rises slowly, according to a speed of the rubber to be vulcanized, substantially equalizes a final vulcanization degree in the whole tread (for example, see Patent Document 1).
As a technique for a tread for a retread tire (precure tread) having a low heat generation effect, for example, Patent Document 2 discloses a technique to make base rubber of a two-layer structure tread low-heat-generating and highly elongated, and Patent Document 3 discloses a technique to use, as bonding cushion rubber for the tread for the retread tire (precure tread), rubber with lower heat generating property than that of rubber used for the tread for the retread tire (precure tread).